Indexable cutting inserts that detachably mounted on tools for cutting workpieces have been known. To improve wear resistance and toughness, many types of indexable cutting inserts each having a structure of a base composed of, for example, a cemented carbide or a cermet, coated with a hard coating composed of, for example, a ceramic material, have been reported.
In such indexable cutting inserts, attempts have been made to improve characteristics by a change in the composition of the hard coating and by the difference of the thickness of the hard coating between on a flank face and on a rake face (Japanese Unexamined Patent Application Publication Nos. 2001-347403 (Patent Document 1), 2004-122263 (Patent Document 2), 2004-122264 (Patent Document 3), and 2004-216488 (Patent Document 4)). High-speed cutting, precision cutting, high-efficiency cutting for difficult-to-cut materials, and the like have been required. However, no indexable cutting insert which has an excellent balance between wear resistance and toughness required for such various types of cutting and which has a surface layer that is substantially prevented from being detached is developed.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-347403    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-122263    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-122264    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-216488